The invention is generally related to printing devices. More particularly, the invention is related to a vacuum control mechanism for improving print media advancement in a printing device.
It is known to use a vacuum induced force to adhere a sheet of print media to a surface in a printing device. For example, a vacuum may be used for holding a sheet of print media temporarily to a platen (e.g., a print media hold-down surface used in a printing device). In a printing device implementation, typically the platen is used either to transport cut-sheet print media to a printing station of a printing device (e.g., printer, photocopier, facsimile, and the like) and/or to hold the print media at the printing station while images are formed at the printing area (e.g., the print zone) of the printing device. Such vacuum hold-down systems are a relatively common, economical technology to implement commercially and can improve throughput specifications.
One universal problem, particularly pertinent in the adaptation of a vacuum hold-down system used in a printing device, is related to print media advancement. When print media advances through a print zone, friction is created between the print media and the platen. The resulting friction can decrease line feed accuracy, which can result in the misalignment of the print media through the print zone and inferior print quality.
A conventional technique for minimizing friction on the platen includes switching a vacuum fan, which generates the vacuum force in a vacuum chamber for holding the print media against the platen, on and off. By switching the vacuum fan off when print media is advancing through a print zone, friction between the print media and the platen is reduced. However, the period of time to pressurize/depressurize a vacuum chamber can have a magnitude in the tens of seconds, which drastically increases printing times. For example, the vacuum fan can typically operate at approximately 9000 rpm to generate the vacuum force. When the fan is switched off, it may continue to spin at a high rpm for a period of time. This increases the time to pressurize the vacuum chamber, and increases print times. Therefore, the throughput of the printing device may be drastically reduced. The period of time to depressurize the chamber when the vacuum fan is switched on may also result in a drastic reduction of throughput for the printing device.
Another conventional technique utilizes two accumulation vacuum chambers having two different vacuum levels (e.g., one chamber having the pressure of the atmosphere and one having a higher pressure for providing more vacuum force to hold down the print media). A switch connects a main vacuum chamber underneath the platen to one of the two accumulation chambers, depending on whether the print media needs to advance or be secured in the print zone. However, the main chamber underneath the platen still needs to pressurize/depressurize depending on which of the two accumulation chambers are connected to the main chamber through the switch. The period of time to pressurize/depressurize the main chamber is dependent on the size of the accumulation chamber connected to the main chamber. Typically, an accumulation chamber is at least twice as large as the main chamber. The use of accumulation chambers may increase the size of the printing device and the cost of the printing device.
In an embodiment of the invention, a method is provided for controlling print media advancement in a printing device. The method comprises steps of substantially sealing a vacuum chamber; depressurizing the vacuum chamber to generate a vacuum force for holding a print media; substantially opening the vacuum chamber to pressurize the vacuum chamber; and advancing the print media.
In another embodiment of the invention a printing device is provided that comprises a vacuum control mechanism for controlling a vacuum force applied to a print media. The vacuum control mechanism is configured to substantially open and close a vacuum chamber to control the vacuum force applied to the print media.
In still another embodiment of the invention, a print media advancement subsystem in a printing device is provided. The print media advancement subsystem comprises a vacuum chamber including a U-shaped vacuum guide, a platen covering the U-shaped vacuum guide and forming the top of the vacuum chamber, and a sealing plate forming a side of the vacuum chamber. The sealing plate is removable to substantially open and substantially seal the vacuum chamber. A vacuum force is applied through the platen to a print media supported by a top surface of the platen when the vacuum chamber is substantially sealed, and the vacuum force is substantially removed from the print media when the vacuum chamber is substantially open. The print media advancement subsystem further comprises a control mechanism connected to the sealing plate and configured to remove the sealing plate from the vacuum chamber in response to receiving a print media advance signal from a controller in the printing device.
In comparison to known prior art, certain embodiments of the invention are capable of achieving certain aspects. For example, certain embodiments provide a print media advancement system that can reduce the cost and size of conventional systems and provide accurate paper advancement that minimizes paper misalignment during printing and increases print quality. Also, certain embodiments provide a robust mechanism that can increase the life of the printing device. Those skilled in the art will appreciate these and other advantages and benefits of various embodiments of the invention upon reading the following detailed description of a preferred embodiment with reference to the below-listed drawings.